Flat-panel displays (FPDs) made in accordance with known active matrix (e.g., TFT, etc.) liquid crystal display technologies (e.g., AMLCD) are typically mounted in front of a back light module which contains an array of fluorescent lamps. AMLCD flat-panel displays of this type have been increasing in size by about 1 to 2 inches diagonal, yearly. The median size in 1999 for use in desktop PCs was about 15 inches diagonal viewing area. A few very large displays are made in the range of 20 to 28 inches diagonal. Tiled AMLCD FPDs may be made in the range of 40 inches diagonal, as described in copending U.S. patent applications Ser. Nos. 09/368,921 1999 (now U.S. Pat. No. 6,657,698) and 09/490,776 (now U.S. Pat. No. 6,680,761). Tiled FPDs, as described in U.S. Pat. No. 5,661,531, require extremely intense back light sources with highly collimated light, masked optical stacks, and pixel apertures that may have low emitted light efficiency. Thus, lighting with unusually high intensity ranges of 50,000 to 150,000 nits is desirable. Also, intensity uniformity over the very large areas of tiled FPDs is very important. Unique back light designs, including temperature control features, are necessary to achieve such high intensities at reasonable power consumption.
Maintaining bright (i.e., high intensity) and uniform illumination of the display over its entire active area is difficult to do. The intensity required for some applications and, in particular, that required for large, tiled, seamless flat-panel LCD displays, causes the lamps to produce a significant amount of heat. In addition, since fluorescent lamps are designed to run most efficiently at an elevated temperature, it is desirable to operate them at or near their ideal design temperature, which is usually about 50 to 60 degrees Centigrade.
Small, edge-lit back light modules, such as those used in notebook or laptop PCs, do not produce sufficient brightness for use in a large area display, nor are they capable of illuminating that large an area uniformly. Thus, it is necessary  preferable to illuminate these larger areas with an array of large fluorescent lamps. The number of lamps required depends on the size of the area to be illuminated and the display brightness requirements. A large area display generally requires multiple lamps to illuminate it properly. A large area display that can be viewed from two sides (i.e., a back-to-back display) requires proportionally more lamps, as well as unique design features to achieve the desired intensities and maintain optimized lamp efficiency through temperature control of the lamps.
Since most displays are designed to be wider than they are tall, it is advantageous, from a reliability and power perspective, to place the lamps in a horizontal orientation. This typically results in the use of fewer lamps and, consequently, lower power consumption, since fewer lamp cathodes are present. The resulting preferred designs orient lamp tubes horizontally, one above the other with predetermined, preferred spacing relationships to each other and to each of the back-to-back displays, one disposed on each side of the lamp array.
It is, therefore, a principal object of the invention to provide a back light module designed to illuminate back-to-back displays.
It is an additional object of the invention to provide a back light module for use with large flat panel displays, either monolithic or tiled.
It is another object of the invention to provide a back light module designed to provide a high intensity light output.
It is a further object of the invention to provide a back light module capable of delivering highly collimated light.
It is an additional object of the invention to provide a back light module having a very high operating efficiency.
It is a still further object of the invention to provide a back light module having a cooling structure to maintain a substantially uniform operating temperature.
It is yet another object of the invention to provide a back light module utilizing an array of horizontally-mounted fluorescent tubes.
It is an additional object of the invention to provide a back light module incorporating a cavity to maximize and control light recirculation.
It is another object of the invention to provide a back light assembly incorporating diffusers, collimators and brightness-enhancing films (BEFs).
It is a further object of the invention to provide a back light assembly suitable for illuminating large, back-to-back, tiled flat-panel displays having visually imperceptible seams.